PLATE XXXVII 



PAGE 

 Figs. 1-4. STROPHOMENA STOSEI Bassler n. sp 250 



1. A brachial valve and interior of a brachial valve nearby. X 2.5. 



2. A pedicle valve of a specimen referred to this species doubtfully on 



account of its high hinge area. X 2.5. 



3. A crushed pedicle valve. X 2.5. 



4. Fragment of a larger shell referred to the species. 



Ordovician (Chazyan), Frederick Is., stone fences just east 

 of Frederick, Maryland. 



Fig. 5. RETEOCBINUS ? sp. undet 209 



A plate-like structure with seven rays. X 6. Other examples exhibit 

 only six rays. None of the specimens shows a basal portion con- 

 necting the rays. 



Ordovician (Chazyan), Frederick Is., just east of Frederick, 

 Maryland. 



Figs. 6-8. ACIDASPIS ULBICHI Bassler n. sp 355 



Three specimens illustrating the unusual development of long spines 

 not only along the free cheeks but even to the tip of the genal 

 spine, and the extraordinary curvature suggesting that the 

 spines were directed over the thorax. X 2. 



Ordovician (Chazyan), Frederick Is., east of Frederick, Mary- 

 land. 



Fig. 9. ISOTELUS sp. undet 345 



Imperfect free cheek. X 1.5. 



Ordovician (Chazyan), Frederick Is., east of Frederick, Mary- 

 land. 



Fig. 10. CAMEROCEKAS sp 321 



Endosiphuncle composed of crystalline matter, embedded in limestone. 

 Ordovician (Chazyan), Frederick Is., east of Frederick, Mary- 

 land. 



387 



